Hard carbon thin film and method of forming the same

ABSTRACT

A hard carbon thin film formed on a substrate has a graded structure in which a ratio of sp 2  to sp 3  carbon-carbon bonding in the thin film decreases in its thickness direction from a thin film/substrate interface toward a surface of the thin film.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a hard carbon thin film and a method offorming the hard carbon thin film.

Description of Related Art

Hard carbon thin films exhibit excellent hardness, resistivity, chemicalstability and the others, and have gathered expectations for theirapplications to functional thin films for electronic devices andsemiconductors, e.g. protective coatings on sliding parts forcompressors such as rotary compressors, protective coatings on bladessuch as electric shaver blades, protective coatings on masks for screendeposition as well as on squeegees, constituent film layers of solarcells, protective coatings on thin film magnetic heads, and protectivecoatings on SAW devices.

In the above applications, poor adhesion of the hard carbon thin film toan underlying layer becomes problematic occasionally. A technique toimprove its adhesion to the underlying layer such as a substrate hasbeen proposed which provides a silicon interlayer between the underlyinglayer and the hard carbon thin film (See, for example, Japanese PatentLaying-Open No. Hei 1-317197 (1989)).

Although the conventional techniques such as mentioned above have apotential advantage of imparting increased adhesion, delamination of thehard carbon thin film from the underlying layer is disadvantageouslyoccasioned when influenced by the internal stress of the hard carbonthin film which becomes greater as a thickness thereof increases. Also,the interlayer must be formed in a separate step which results in acomplicated fabrication.

In view of the above, there has been a continuing need for a hard carbonthin film which is capable of exhibiting an improved adherence to anunderlying layer such as a substrate.

A crystalline hard carbon thin film, as generally called a diamond thinfilm, is typically formed through thermal decomposition of a materialgas such as methane using a hot filament. Such a technique is howeveraccompanied by the elevation of a substrate temperature up to about1000° C. which limits the material type of a substrate to be used. Also,the diamond thin film thus formed generally exhibits a large surfaceirregularity, which necessitates post-polishing thereof to smooth thesurface, such as for use as a surface acoustic wave device.

A diamond-like thin film mainly consisting of non-crystalline oramorphous components has also been known as illustrative of the hardcarbon thin film. Such a diamond-like thin film is generally formedusing a plasma CVD technique which permits the formation thereof at areduced substrate temperature around a room temperature. Thediamond-like thin film thus formed is superior in surface smoothness butis generally inferior in surface hardness to the diamond thin film.

Accordingly, there remain a need for a technique which is capable offorming diamond thin films having smaller surface irregularities atreduced substrate temperatures, and another need for a technique whichis capable of forming diamond-like thin films having increased surfacehardnesses. Such needs would be met if a technique is provided which cancontrol to some extent those mechanical properties of the diamond anddiamond-like thin films to form hard carbon thin films with tailoredproperties. However, such a technique has not been reported up to date.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a hard carbon thinfilm which exhibits a satisfactory hardness as well as a good adhesionto an underlying layer such as a substrate, and a method of forming thehard carbon thin film.

It is another object of the present invention to provide a method forforming a hard carbon thin film which can control a proportion ofcrystalline and non-crystalline components in the thin film as well asits film properties such as hardness and surface smoothness.

A hard carbon thin film in accordance with a first aspect of the presentinvention characteristically has a graded structure in which a ratio ofsp² to sp³ carbon-carbon bonding (hereinafter referred to as "sp² /sp³ratio") in the thin film decreases in its thickness direction from afilm/underlayer interface toward a surface of the thin film.

A hard carbon thin film in accordance with a second aspect of thepresent invention comprises two or more layers having respectiveindividual sp² /sp³ ratios different from each other, so that the sp²/sp³ ratio in the thin film decreases in a stepwise manner in itsthickness direction from a film/underlayer interface toward a surface ofthe thin film.

A hard carbon thin film in accordance with a second aspect of thepresent invention characteristically has a graded structure in which thesp² /sp³ ratio in the thin film in its thickness direction decreasesfrom a film/underlayer interface to a minimum and increases therefromtoward a surface of the thin film.

A hard carbon thin film in accordance with a fourth aspect of thepresent invention characteristically comprises three or more layershaving respective individual sp² /sp³ ratios different from each other,so that the sp² /sp³ ratio in the thin film decreases in a stepwisemanner in its thickness direction from a film/underlayer interface to aminimum and increases therefrom in a stepwise manner toward a surface ofthe thin film.

The sp² and sp³ carbon-carbon bondings indicate different forms ofchemical bonding between carbon atoms. It is generally known that thecarbon-carbon bonding in the diamond thin film is predominantly sp³while that in a graphite is predominantly sp². It is also known that anamorphous diamond-like carbon thin film, as well as a partiallycrystalline diamond-like carbon thin film, may have a structure in whichboth sp² and sp³ carbon-carbon bondings are distributed therethrough. Inthe present invention, such a sp² /sp³ ratio is characteristicallyvaried in a film thickness direction as described earlier.

In the present invention, the sp² /sp³ ratio is varied preferably in therange of 0-3. Accordingly, the present invention is intended to includethe case where the sp² /sp³ ratio is zero, i.e., the carbon-carbonbonding in the thin film is essentially devoid of sp² and predominantlyof sp³.

In general, the increased sp² /sp³ ratio, accordingly the increasedproportion of sp² carbon-carbon bonding tends to cause a decrease ininternal stress to provide better adhesion to an underlying layer suchas a substrate. On the other hand, the reduced sp² /sp³ ratio,accordingly the increased proportion of sp³ carbon-carbon bonding tendsto produce a film with increased hardness and internal stress.

The sp² /sp³ ratio as specified in the present invention can bedetermined such as by an electron energy loss spectroscopy (EELS).

In the present invention, the hard carbon thin film is contemplated toinclude a crystalline diamond carbon thin film, an amorphousdiamond-like carbon thin film, and a diamond-like carbon thin filmhaving a partial crystalline structure. Accordingly, the change of sp²/sp³ ratio in a thickness direction of a thin film may be accompanied bythe change in proportion of crystalline and non-crystalline componentsin the thickness direction of the film.

The hard carbon thin film according to the present invention can beformed using generally-employed film-forming techniques. Foremost amongthose techniques are plasma CVD techniques including an ECR plasma CVDtechnique. A hot-filament CVD technique may also be used. Suchtechniques as to physically form thin films may also be applicable whichinclude a sputtering technique and an ion beam deposition techniqueusing an ion gun. Furthermore, the thin film may be formed using anycombination of the above-mentioned plasma CVD, hot-filament CVD,sputtering and ion-beam deposition techniques.

The hard carbon thin film of the present invention may be formed on anunderlying layer such as a substrate through an interlayer interposedtherebetween. The material types of the interlayer include Si, Ti, Zr,W, Mo, Ru, Ge and oxides, nitrides and carbides thereof. The interlayerscomprised of such materials can be formed such as by a magnetron RFsputtering technique. For example, any of those metallic elements can besputtered in an argon plasma to form the interlayer. An oxygen ornitrogen gas may be introduced into a chamber during the sputtering toform the interlayer comprised of oxides or nitrides of any of thoseelements. The interlayer is formed to a typical thickness in the rangeof 20Å-300Å.

A first method for forming the hard carbon thin film of the presentinvention using a plasma CVD technique is characterized in that ionspecies, associated with formation of the thin film, in a plasma arevaried in kinetic energy with film-forming time, so that the sp² /sp³ratio in the hard carbon thin film is varied in its thickness direction.In order to vary the kinetic energies of those ion species, anacceleration voltage may be applied to them by applying a voltage to agrid disposed between a plasma generation chamber and a substrate, forexample.

A second method for forming the hard carbon thin film of the presentinvention using a plasma CVD technique is characterized in that a variedamount of a hydrogen gas is admitted to a reaction system for its changewith film-forming time, so that the sp² /sp³ ratio in the thin film isvaried in its thickness.

A third method for forming the hard carbon thin film of the presentinvention using a plasma CVD technique is characterized in that asubstrate temperature is varied with film-forming time, so that the sp²/sp³ ratio in the thin film formed on the substrate is varied in itsthickness direction.

A fourth method for forming the hard carbon thin film of the presentinvention using a plasma CVD technique is characterized in that theproportion of ion species associated with formation of the thin film isvaried with film-forming time, so that the sp² /sp³ ratio in the thinfilm is varied in its thickness direction. Those ion species associatedwith formation of the thin film include CH₃ ⁺ and CH₂ ⁺, for example.The sp² /sp³ ratio in the thin film can be varied in its thicknessdirection by varying the proportion of those ion species withfilm-forming time.

The above-described first through fourth methods may be performedindependently or in any combination thereof.

Furthermore, the hard carbon thin film of the present invention can beformed using a technique in accordance with a fifth aspect of thepresent invention which will be described hereinafter.

The film-forming method of the present invention characteristicallyutilizes a plasma CVD process in varying the ion species associated withformation of the thin film to thereby varying the composition orstructure of the thin film in its thickness direction. The compositionor structural gradient in a thickness direction of the thin film can beproduced such as by varying the sp² /sp³ ratio in a thickness directionof the thin film, e.g., by varying the ion species, such as CH₃ ⁺ andCH₂ ⁺ as described above as being associated with formation of the thinfilm, with film-forming time.

In accordance with a fifth aspect of the present invention, a method isprovided for forming a hard carbon thin film through decomposition of amaterial gas. A characteristic feature of the method is that thematerial gas is decomposed using a technique of exposing them to heator/and to a plasma whereby the film properties of the resulting hardcarbon thin film can be controlled.

The method in accordance with the fifth aspect of the present inventioncombines a thermal decomposition technique, which is suited forformation of hard carbon thin films having higher degrees ofcrystallinity such as diamond thin films, and a plasma-assisteddecomposition technique which is suited for formation of hard carbonthin films having a major proportion of amorphous components such asdiamond-like thin films, to thereby control a proportion of crystallineand non-crystalline components in the hard carbon thin film andaccomplish the control of its film properties such as hardness andsurface smoothness.

Illustrative of the thermal decomposition technique is a technique whichthermally decomposes the material gas by exposing them to heat from ahot filament disposed above a substrate on which the hard carbon thinfilm is to be deposited.

Exemplary techniques of forming the hard carbon thin films throughplasma-assisted decomposition of the material gas includegenerally-employed plasma CVD, radio-frequency (RF) plasma CVD, DCplasma CVD, and electron cyclotron resonance (ECR) plasma CVDtechniques. The ECR plasma CVD technique is preferred when desired toform wide-area hard carbon thin films.

In one embodiment practicing the method in accordance with the fifthaspect of the present invention, the film formation through the thermaldecomposition of the material gas is followed by the additional filmformation through the plasma-assisted decomposition of the material gas.As discussed earlier, the use of thermal decomposition technique iseffective in forming the hard carbon thin film having a higher degree ofcrystallinity. The succeeding film formation thereon using theplasma-assisted decomposition technique is affected by the higher degreeof crystallinity of the underlying hard carbon thin film to result information of the additional hard carbon thin film having an increaseddegree of crystallinity or hardness as a whole.

In another embodiment practicing the method in accordance with the fifthaspect of the present invention, the film formation through the thermaldecomposition of the material gas is effected while the film formationthrough the plasma-assisted decomposition of the material gas is inprogress. Such a simultaneous occurrence of the thermal andplasma-assisted decomposition of the material gas results in formationof the hard carbon thin film having a higher degree of crystallinity orhardness than when formed solely through the plasma-assisteddecomposition of the material gas.

In the fifth aspect of the present invention, whether the hard carbonthin film formed has a crystalline diamond nature or an amorphousdiamond-like nature depends upon the film-forming conditionsrespectively through the thermal decomposition and plasma-assisteddecomposition of the raw material gas. Accordingly, the suitable controlof these film-forming conditions results in formation of the hard carbonthin film having tailored film properties.

Also, whether the hard carbon thin film formed has a crystalline diamondnature or an amorphous diamond-like nature can be determined such as bya Raman spectroscopy, as will be described hereinafter.

In a further narrowed aspect of the present invention, a method forforming a hard carbon thin film comprises a first step and a subsequentsecond step. In the first step, a hard carbon thin film is formed usinga first technique incorporating at least a film-forming techniquethrough thermal decomposition of a material gas. The first step isfollowed by the second step in which an additional hard carbon thin filmis formed thereon using a second technique incorporating at least afilm-forming technique through decomposition of the material gas by aplasma.

In the first step, a hard carbon thin film is formed by using the firsttechnique incorporating at least the film-forming technique throughthermal decomposition of a material gas. Accordingly, the hard carbonthin film may be formed by solely using the film-forming techniquethrough thermal decomposition of the material gas. If desired, the firsttechnique may further incorporate another film-forming technique, suchas the film-forming technique through plasma-assisted decomposition ofthe material gas, for simultaneous practice with the film-formingtechnique through thermal decomposition of the material gas.

In the second step, the additional hard carbon thin film is formedthereon using the second technique incorporating at least thefilm-forming technique through plasma-assisted decomposition of thematerial gas. Accordingly, a hard carbon thin film may be formed bysolely using the film-forming technique through plasma-assisteddecomposition of the material gas. If desired, the second technique mayfurther incorporate another film-forming technique, such as thefilm-forming technique through thermal decomposition of the materialgas, for simultaneous practice with the film-forming technique throughplasma-assisted decomposition of the material gas.

Since in the first step, the hard carbon thin film is formed by usingthe first technique incorporating at least the film-forming techniquethrough thermal decomposition of the material gas, a relatively highdegree of crystallinity can be imparted to the resulting hard carbonthin film. In the second step, the second technique is used to form theadditional hard carbon thin film on the hard carbon thin film having thehigher degree of crystallinity resulting from the first step, so thatthe relatively high degree of crystallinity of the underlying hardcarbon thin film favorably affects the succeeding formation of theadditional hard carbon thin film in the second step. Therefore, the hardcarbon thin film can be formed which has a relatively high degree ofcrystallinity or hardness as a whole. Also, since the second techniqueincorporates at least the film-forming technique through plasma-assisteddecomposition of the material gas, amorphous components may be producedin the overlying hard carbon thin film formed by using the secondtechnique, thereby imparting a relatively good surface smoothness,approaching at best to that of the diamond-like thin film, to theresulting hard carbon thin film.

In accordance with the present aspect, the second techniqueincorporating at least the film-forming technique throughplasma-assisted decomposition of the material gas at a relatively lowtemperature, when practiced subsequent to the first techniqueincorporating at least the film-forming technique through thermaldecomposition of the material gas, imparts a smooth surface as well asan increased degree of crystallinity or hardness as a whole to theoverlying hard carbon thin film.

In the fifth aspect of the present invention, in addition to admittingthe material gas, a method further admits a hydrogen gas to a reactionsystem to thereby control film properties of the resulting hard carbonthin films. Introduction of the hydrogen gas contributes to removal ofgraphite components to permit selective formation of diamond thin filmswhich have higher degrees of crystallinity and hardness.

Also in the fifth aspect of the present invention, a hard carbon thinfilm is formed on a substrate through an interlayer providedtherebetween. The formation of the hard carbon thin film through theinterlayer improves its characteristics, e.g. adhesion or adherence tothe substrate. The interlayer may be comprised of a thin film of Si, Ti,Zr, Ge, or oxides or nitrides thereof. The film thickness of theinterlayer is not particularly specified, but is preferably in the rangeof 20Å-1000Å.

In a sixth aspect of the present invention, a method is provided whichforms an amorphous carbon coating on a substrate. Characteristically, asubstrate is at its surface cleaned prior to formation of the hardcarbon thin film thereon, and/or the hard carbon thin film is at itsgrowth surface cleaned during formation thereof. The precleaning of thesubstrate serves to remove dusts, surface irregularities and scratches,which if present, provide undesirable growth surfaces on the substrate,to assure an uniform growth of the amorphous carbon coating on thesubstrate. Also, the cleaning or etching during coating formation servesto eliminate irregularity or unevenness of the coating growth surface tofurther insure the uniform growth of the amorphous carbon coating.

Ion or energy beam irradiation may be effected to clean the substratesurface prior to coating formation and/or the coating growth surfaceduring the coating formation. In the ion beam irradiation, inert gasions such as an Ar gas ion may be emitted such as by an ion gun. Thecondition of ion beam emission is not particularly specified, butgenerally at an ion current density of 0.01-5 mA/cm², an accelerationvoltage of 20-10,000 eV, and an inert gas partial pressure of 1×10⁻⁶-1×10⁻¹ Torr.

An electron or laser beam may be employed to effect the energy beamirradiation. The electron beam may be emitted under a typical currentdensity condition of 1×10⁻² -1×10¹ A/cm². The laser beam may be emittedunder a typical power density condition of 1×10⁻³ -1×10⁸ W/cm². Laserbeam sources include excimer, argon, YAG, CO², He--Cd, semiconductor,ruby lasers. Such an energy beam is generally scanned over the substratesurface or the coating growth surface. The energy beam may be providedin a pulsed form, if necessary.

Also in the sixth aspect of the present invention, in order for thesubstrate surface to be cleaned, the substrate may be irradiated with aplasma prior to coating formation thereon. The plasma may be an inertgas plasma, for example. A voltage may be applied to the substrate foracceleration of the produced plasma onto the substrate. For example, aradio-frequency voltage may be applied to the substrate so that anegative voltage is generated in the substrate which preferably has anabsolute value of 20 V or higher.

In the case where the cleaning or etching is effected during coatingformation, such a treatment preferably completes after the lapse ofabout one tenth of a total film-forming process from the start ofcoating formation.

For the method for forming an amorphous carbon film in accordance withthe sixth aspect of the present invention, applicable film-formingtechniques include general vapor phase epitaxial techniques, e.g., CVDtechniques as represented by plasma CVD techniques such as the ECRplasma CVD technique and hot-filament CVD technique, sputtering andvacuum deposition techniques.

In accordance with the sixth aspect of the present invention, thesurface cleaning treatment either prior to or during coating formationresults in formation of an amorphous carbon coating which exhibits asurface roughness h_(rms) not exceeding one fifth of a thicknessthereof. Under a selected cleaning condition, an amorphous carboncoating may be formed which exhibit a surface roughness h_(rms) notexceeding one tenth of a thickness thereof. The values of surfaceroughness has can be determined by using a stylus-based technique, andindicated by root-mean-square deviations from a mean surface.

An amorphous carbon coating in accordance with the sixth aspect of thepresent invention characteristically exhibits, immediately afterformation thereof, a surface roughness h_(rms) not exceeding one fifth,preferably one tenth of a thickness thereof. The amorphous carboncoating in accordance with the sixth aspect of the present inventionexhibits such a surface roughness immediately after formation thereof,i.e., before any post-processing, such as polishing, is applied to acoating surface immediately after formation thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of one embodiment of a hardcarbon thin film in accordance with a first aspect of the presentinvention;

FIG. 2 is a graph showing a varied sp² /sp³ ratio in a thicknessdirection of the hard carbon thin film shown in FIG. 1;

FIG. 3 is a schematic cross-sectional view of one embodiment of a hardcarbon thin film in accordance with a second aspect of the presentinvention;

FIG. 4 is a graph showing a varied sp² /sp³ ratio in a thicknessdirection of the hard carbon thin film shown in FIG. 3;

FIG. 5 is a graph showing a varied sp² /sp³ ratio in a thicknessdirection of one embodiment of a hard carbon thin film in accordancewith a third aspect of the present invention;

FIG. 6 is a graph showing a varied sp² /sp³ ratio in a thicknessdirection of one embodiment of a hard carbon thin film in accordancewith a fourth aspect of the present invention;

FIG. 7 is a schematic constituent diagram of an exemplary ECR plasma CVDapparatus for forming hard carbon thin films in accordance with thepresent invention;

FIG. 8 is a graph showing a first exemplary pattern of an accelerationvoltage varied with film-forming time for application to a grid inaccordance with one embodiment of the present invention;

FIG. 9 is a graph showing a first exemplary pattern of a supplypressure, varied with film-forming time, to which a hydrogen gas isadmitted in a reaction system in accordance with one embodiment of thepresent invention;

FIG. 10 is a graph showing a second exemplary pattern of an accelerationvoltage varied with film-forming time for application to a grid inaccordance with another embodiment of the present invention;

FIG. 11 is a graph showing a second exemplary pattern of a supplypressure, varied with film-forming time, to which a hydrogen gas isadmitted in a reaction system in accordance with another embodiment ofthe present invention;

FIG. 12 is a graph showing a substrate temperature varied withfilm-forming time in accordance with one embodiment of the presentinvention;

FIG. 13 is a graph showing a third exemplary pattern of an accelerationvoltage varied with film-forming time for application to a grid inaccordance with still another embodiment of the present invention;

FIG. 14 is a graph showing a third exemplary pattern of a supplypressure, varied with film-forming time, to which a hydrogen gas isadmitted in a reaction system in accordance with still anotherembodiment of the present invention;

FIG. 15 is a graph showing a fourth exemplary pattern of an accelerationvoltage varied with film-forming time for application to a grid inaccordance with still another embodiment of the present invention;

FIG. 16 is a graph showing a fourth exemplary pattern of a supplypressure, varied with film-forming time, to which a hydrogen gas isadmitted in a reaction system in accordance with still anotherembodiment of the present invention;

FIG. 17 is a schematic cross-sectional view of an exemplary film-formingapparatus for embodying a method in accordance with a fifth aspect ofthe present invention;

FIG. 18 is a schematic cross-sectional view of the apparatus of FIG. 17wherein a substrate holder is so rotated as for a substrate to facetoward a target;

FIG. 19 is a schematic cross-sectional view of another exemplaryfilm-forming apparatus for embodying the method in accordance with thefifth aspect of the present invention;

FIG. 20 is a schematic cross-sectional view of an exemplary amorphouscoating forming apparatus for embodying a method in accordance with asixth aspect of the present invention; and

FIG. 21 is a graph showing a relationship between surface roughness ofamorphous carbon coatings formed in accordance with the sixth aspect ofthe present invention and a time period during which a substrate isexposed to ion radiation for cleaning thereof prior to formation of theamorphous carbon coatings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a schematic cross-sectional view of one embodiment of a hardcarbon thin film in accordance with a first aspect of the presentinvention. Formed on a substrate 1 is a hard carbon thin film 2.

FIG. 2 is a graph showing the changes of sp² /sp³ ratio in a thicknessdirection of the hard carbon thin film 2 of FIG. 1. As shown in FIG. 2,the sp² /sp³ ratio decreases in the thickness direction of the film,i.e., toward its surface from a film/substrate interface. It followsthat the hard carbon thin film 2 has an increased sp² /sp³ ratio andaccordingly a reduced internal stress in the vicinity of thefilm/substrate interface, and has good adhesion to the substrate 1.Also, the hard carbon thin film 2 has a decreased sp² /sp³ ratio andaccordingly increased hardness and internal stress in the vicinity ofits surface.

FIG. 3 is a schematic cross-sectional view of one embodiment of a hardcarbon thin film in accordance with a second aspect of the presentinvention. Formed on the substrate 1 is a hard carbon thin film 3comprised of plural layers 3a through 3e stacked on the substrate 1.

FIG. 4 is a graph showing the changes of sp² /sp³ ratio in a thicknessdirection of the hard carbon thin film 3 of FIG. 3. As shown in FIG. 4,the sp² /sp³ ratio decreases in a stepwise manner from layer to layer inthe thickness direction of the film, i.e., toward its surface from afilm/substrate interface. As can be seen from FIG. 4, in this particularembodiment, each layer has a substantially uniform sp² /sp³ ratiothrough its thickness, and the layers are stacked on the substrate in asequence of decreasing sp² /sp³ ratio to constitute the hard carbon thinfilm 3. The lower-most layer 3a adjacent to the substrate 1 comprises acomposition having the greatest sp² /sp³ ratio and accordingly the leastinternal stress for better adherence to the substrate 1. The upper-mostlayer 3e adjacent to the surface of the hard carbon thin film 3comprises a composition having the least sp² /sp³ ratio and accordinglythe greatest internal stress and hardness.

FIG. 5 is a schematic cross-sectional view of one embodiment of a hardcarbon thin film in accordance with a third aspect of the presentinvention. A hard carbon thin film in accordance with the presentembodiment is formed on a substrate in the same manner as the embodimentshown in FIG. 1. The sp² /sp³ ratio gradually decreases from asubstrate/film interface to a minimum at an intermediate of the thinfilm, and then increases therefrom toward a surface of the thin film.Accordingly, the hard carbon thin film comprises compositions having thegreater sp² /sp³ ratios and the less internal stresses in the respectivevicinities of the substrate/film interface and the film surface. Thehard carbon thin film is at its intermediate less in the sp² /sp³ ratio,and accordingly higher in both film hardness and internal stress. As aresult, the hard carbon thin film has a smooth surface due to thegreater sp² /sp³ ratio.

FIG. 6 is a schematic cross-sectional view of one embodiment of a hardcarbon thin film in accordance with a fourth aspect of the presentinvention. A hard carbon thin film of this embodiment is constructed bystacking plural layers 3a through 3e on the substrate 1 in the samemanner as the embodiment shown in FIG. 3. As can be seen from FIG. 6,the sp² /sp³ ratio decreases in a stepwise manner from a lower-mostlayer adjacent to a substrate/film interface to a minimum at anintermediate layer, and then increases therefrom in a stepwise mannertoward an upper-most layer adjacent to a surface of the thin film.Accordingly, the lower-most and upper-most layers have the greater sp²/sp³ ratios and the lower internal stresses, respectively. Theintermediate layer has the least sp² /sp³ ratio, and accordingly thehigher film hardness and internal stress. Also, the hard carbon thinfilm has an extremely smooth surface for its greater sp² /sp³ ratio. Asa result, the hard carbon thin film in accordance with the fourth aspecthas a smooth surface due to the greater sp² /sp³ ratio and is still highin its overall hardness.

FIG. 7 is a schematic cross-sectional view showing an exemplary ECRplasma CVD apparatus which is capable of forming the hard carbon thinfilm of the present invention. Referring to FIG. 7, a vacuum chamber 18has a plasma generation chamber 14 to which one end of a waveguide 12 isconnected. Another end of the waveguide 12 is mounted to a microwavesupplying means 11. A microwave generated in the microwave supplyingmeans 11 passes through the waveguide 12 and a microwave inlet window 13to be guided into the plasma generation chamber 14.

The plasma generation chamber 14 is provided with a gas inlet line 15for introducing a discharge gas such as argon (Ar), as well as a rawmaterial gas such as methane (CH₄) or hydrogen (H₂), into the plasmageneration chamber 14. Also, a plurality of plasma magnetic fieldgenerators 16 are mounted circumferentially of the plasma generationchamber 14. A high density ECR plasma can be generated within the plasmageneration chamber 14 through the interaction of a high-frequencymagnetic field produced by the microwave and a magnetic field generatedby the plasma magnetic field generators 16.

The vacuum chamber 18 encloses a substrate holder 17 on which asubstrate 10 is placed. In this embodiment, employed as the substrate 10is a sliding part of a rotary compressor, i.e., a vane (made ofhigh-speed tool steel).

Located in an area between the plasma generation chamber 14 and thesubstrate 10 is a grid 19 to which a cathode of a direct-current powersource 20 is connected for applying a negative voltage to the grid 19.The application of negative voltage to the grid 19 imparts anaccelerating energy to positive ions in the plasma within the plasmageneration chamber 14 so that the positive ions are accelerated onto thesubstrate 10. Therefore, the ion kinetic energy in the plasma can becontrolled by regulating the voltage to be applied to the grid. Inspecific, the ion kinetic energy can be increased by applying anincreased acceleration voltage to the grid 19.

EXAMPLE 1

The apparatus shown in FIG. 7 is employed to form a hard carbon thinfilm having a graded structure in which the sp² /sp³ ratio decreasescontinuously in a uniform manner in a thickness direction of the film,i.e., toward its surface from a film/substrate interface.

The vacuum chamber 18 is first evacuated to a pressure of 10⁻⁵ -10⁻⁷Torr. Then, Ar and CH₄ gases are introduced into the plasma generationchamber 14 at respective pressures of 2.5×10⁻⁴ Torr. and 3.0×10⁻⁴ Torr.to convert them into plasmas within the plasma generation chamber 14.

Next, the varying acceleration voltage is applied to the grid 19 in sucha controlled fashion that it is maintained at 2 kV for the first oneminute period at the initial stage of film formation and decreased withfilm-forming time to a final value of 200 V, as shown in FIG. 8.Concurrently, an H₂ gas is introduced through the gas inlet line 15 intothe plasma generation chamber 14 in such a controlled fashion that itssupply pressure starts to rise after the lapse of one minute at theinitial stage of film formation and continuously increases withfilm-forming time to a final value of 5.0×10⁻³ Torr., as shown in FIG.9.

A hard carbon thin film is thus formed on the substrate 10. The obtainedhard carbon thin film was measured for the sp² /sp³ ratios in itsthickness direction by an electron energy loss spectroscopy (EELS). As aresult, the sp² /sp³ ratio was found to be 3 for thesubstrate-neighboring film portion formed during the first one minuteperiod at the initial stage of film formation while the sp² /sp³ ratiowas found to be zero for the film surface portion in which the C--Cbonding was essentially devoid of sp² and predominantly sp³. Also, thesubstrate-neighboring film portion was found as comprising amorphousdiamond-like carbon while the film surface portion as comprisingcrystalline diamond.

The surface portion of the hard carbon thin film obtained was measuredfor hardness to reveal a value of 7000 Hv (Vickers hardness). Forcomparative purposes, the acceleration voltage applied to the grid wasmaintained at 2 kV from the start till the completion of film formationto form a hard carbon thin film of Comparative Example 1-1 which wasmeasured for hardness to reveal a value of 4000 Hv.

Also, in order to evaluate the adherence of the obtained hard carbonthin film to the substrate, a constant load (2 kg) indentation test wascarried out using a Vickers penetrator. Fifty sample pieces were usedfor the test, and the number of sample pieces which showed delaminationwas counted as indicating the level of adherence of the hard carbon thinfilm. For comparative purposes, a hard carbon thin film of ComparativeExample 1-2 was formed with no acceleration voltage applied to the gridduring film formation, which was duly subjected to the indentation testusing a Vickers penetrator as similar to the above. The number of samplepieces which showed delamination was found to be 0 for the hard carbonthin film of Example 1 according to the present invention, and 26 forthe hard carbon thin film of Comparative Example 1-2.

As can be appreciated from the foregoing, in addition to being high inhardness, the hard carbon thin film in accordance with the presentinvention is excellent in adherence.

EXAMPLE 2

The apparatus shown in FIG. 7 is employed to form a hard carbon thinfilm having a graded structure in which the sp² /sp³ ratio decreases ina stepwise manner (one step in this Example) in a thickness direction ofthe film, i.e., toward its surface from a film/substrate interface.

The vacuum chamber 18 is first evacuated to a pressure of 10⁻⁵ -10⁻⁷Torr. Then, Ar and CH₄ gases are introduced into the plasma generationchamber 14 at respective pressures of 2.5×10⁻⁴ Torr. and 3.0×10⁻⁴ Torr.to convert them into plasma within the plasma generation chamber 14.

Next, the varying acceleration voltage is applied to the grid 19 in sucha controlled fashion that it is maintained at 2 kV for the first oneminute period at the initial stage of film formation and thereaftermaintained at 200 V until the completion of film formation, as shown inFIG. 10. Concurrently, an H₂ gas is introduced through the gas inletline 15 into the plasma generation chamber 14. As shown in FIG. 11, theH₂ gas supply is commenced after the lapse of one minute period at theinitial stage of film formation and thereafter maintained at 5.0×10⁻³Torr. until the completion of film formation.

A hard carbon thin film is thus formed on the substrate 10. The obtainedhard carbon thin film was measured for the sp² /sp³ ratios in itsthickness direction by an electron energy loss spectroscopy (EELS). As aresult, the sp² /sp³ ratio was found to be 3 for thesubstrate-neighboring film portion formed during the first one minuteperiod at the initial stage of film formation, while the sp² /sp³ ratiowas found to be zero for the remaining overlying film portion in whichthe C--C bonding was essentially devoid of sp² and predominantly sp³.Also, the substrate-neighboring film portion was found as comprisingamorphous diamond-like carbon while the remaining overlying film portionas comprising crystalline diamond carbon.

The surface portion of the hard carbon thin film obtained was measuredfor hardness to reveal a value of 8000 Hv. For comparative purposes, theacceleration voltage applied to the grid was maintained at 2 kV from thestart till the completion of film formation to form a hard carbon thinfilm of Comparative Example 2-1 which was measured for hardness toreveal a value of 4000 Hv.

Also, in order to evaluate the adherence of the obtained hard carbonthin film to the substrate, a constant load (2 kg) indentation test wascarried out using a Vickers penetrator. Fifty sample pieces were usedfor the test, and the number of sample pieces which showed delaminationwas counted as indicating the level of adherence of the hard carbon thinfilm. For comparative purposes, a hard carbon thin film of ComparativeExample 2-2 was formed with no acceleration voltage applied to the gridduring film formation, which was duly subjected to the indentation testusing a Vickers penetrator as similar to the above. The number of samplepieces which showed delamination was found to be 0 for the hard carbonthin film of Example 2 according to the present invention, and 26 forthe hard carbon thin film of Comparative Example 2-2.

As can be appreciated from the foregoing, in addition to being high inhardness, the hard carbon thin film in accordance with the presentinvention is excellent in adherence.

EXAMPLE 3

The apparatus shown in FIG. 7 is employed to form a hard carbon thinfilm having a graded structure in which the sp² /sp³ ratio decreasescontinuously in a uniform manner in a thickness direction of the film,i.e., toward its surface from a film/substrate interface.

The vacuum chamber 18 is first evacuated to a pressure of 10⁻⁵ 10⁻⁷Torr. Then, Ar and CH₄ gases are introduced into the plasma generationchamber 14 at respective pressures of 2.5×10⁻⁴ Torr. and 3.0×10⁻⁴ Torr.to convert them into respective gas plasmas within the plasma generationchamber 14.

The constant acceleration voltage of 1 kV is applied to the grid 19during film formation.

As shown in FIG. 12, a substrate temperature is set at 20° C. (roomtemperature) for the first one minute period at the initial stage offilm formation. After the one minute period, heating is applied toincrease the substrate temperature so that it approaches about 800° C.when 3 minutes elapse from the start of film formation. The substratetemperature is thereafter maintained at 800° C. until the completion offilm formation. Besides, an H₂ gas is introduced into the plasmageneration chamber 14, which is maintained at 5.0×10⁻³ Torr. during filmformation.

A hard carbon thin film is thus formed on the substrate 10. The obtainedhard carbon thin film was measured for the sp² /sp³ ratios in itsthickness direction by an electron energy loss spectroscopy (EELS). As aresult, the sp² /sp³ ratio was found to be 3 for thesubstrate-neighboring film portion formed during the first one minuteperiod at the beginning of film formation, while the sp² /sp³ ratio wasfound to be zero for the remaining overlying film portion in which theC--C bonding was essentially devoid of sp² and predominantly sp³. Also,the substrate-neighboring film portion was found as comprising amorphousdiamond-like carbon while the remaining overlying film portion ascomprising crystalline diamond carbon.

The surface portion of the hard carbon thin film obtained was measuredfor hardness to reveal a hardness of 7000 Hv.

Also, in order to evaluate the adherence of the obtained hard carbonthin film to the substrate, a constant load (2 kg) indentation test wascarried out using a Vickers penetrator. Fifty sample pieces were usedfor the test, and the number of sample pieces which showed delaminationwas counted as indicating the level of adherence of the hard carbon thinfilm. The results demonstrated that no sample piece showed delamination.

As can be appreciated from the foregoing, in addition to being high inhardness, the hard carbon thin film in accordance with the presentinvention is excellent in adherence.

EXAMPLE 4

In this Example, the apparatus shown in FIG. 7 is employed to form ahard carbon thin film having a graded structure in which the sp² /sp³ratio once decreases from a substrate/film interface to a minimum at anintermediate thickness of the thin film, and then increases therefromtoward a surface of the thin film.

The vacuum chamber 18 is first evacuated to a pressure of 10⁻⁵ -10⁻⁷Torr. Then, Ar and CH₄ gases are introduced into the plasma generationchamber 14 at respective pressures of 2.5×10⁻⁴ Torr. and 3.0×10⁻⁴ Torr.to convert them into respective gas plasmas within the plasma generationchamber 14.

Next, the varying acceleration voltage is applied to the grid 19 in sucha controlled fashion that it is maintained at 2 kV for the first oneminute period at the initial stage of film formation, decreased withfilm-forming time to a minimum value of 200 V when 10 minutes elapsefrom the start of film formation, and increased to a final value of 2kV, as shown in FIG. 13. Concurrently, an H₂ gas is introduced into theplasma generation chamber 14 by varying its supply pressure in such acontrolled fashion that it starts to increase with film-forming timeafter the lapse of one minute period at the initial stage of filmformation, reaches a maximum value of 5.0×10⁻³ Torr. when 10 minuteselapse from the start of film formation, and decreases with film-formingtime to zero one minute before the completion of film formation, asshown in FIG. 14.

A surface portion of the hard carbon thin film thus formed was measuredfor hardness to reveal a value of 6000 Hv, and also determined forsurface roughness (R_(max)) to reveal a value of 20 Å, when measured bya surface roughness tester, which accounted for an extremely smoothsurface of the hard carbon thin film.

EXAMPLE 5

In this Example, the apparatus shown in FIG. 7 is employed to form ahard carbon thin film having a graded structure in which the sp² /sp³ratio once decreases in a stepwise manner from a substrate/filminterface to a minimum at an intermediate thickness of the thin film,and then increases therefrom in a stepwise manner toward a surface ofthe thin film.

The vacuum chamber 18 is first evacuated to a pressure of 10⁻⁵ -10⁻⁷Torr. Then, Ar and CH₄ gases are introduced into the plasma generationchamber 14 at respective pressures of 2.5×10⁻⁴ Torr. and 3.0×10⁻⁴ Torr.to convert them into plasma within the plasma generation chamber 14.

Next, the varying acceleration voltage is applied to the grid 19 in sucha stepwise manner that it is maintained at 2 KV during an initial4-minute film-forming period, at 1 kV during a second 4-minutefilm-forming period, at 200 V during a third 4-minute film-formingperiod, at 1 kV during a fourth 4-minute film-forming period, and at 2kV during a final 4-minute film-forming period, as shown in FIG. 15.Concurrently, an H₂ gas is introduced into the plasma generation chamber14 by varying its supply pressure in such a stepwise manner that it ismaintained at zero during the initial 4-minute film-forming period, at2.5×10⁻³ Torr. during the second 4-minute film-forming period, at5.0×10⁻³ Torr. during the third 4-minute film-forming period, at2.5×10⁻³ Torr. during the fourth 4-minute film-forming period, and atzero during a final 4-minute film-forming period, as shown in FIG. 16.

A surface portion of the hard carbon thin film thus formed was measuredfor hardness to reveal a value of 7000 Hv, and also determined forsurface roughness (R_(max)) to reveal a value of 20 Å, when measured bya surface roughness tester, which accounted for an extremely smoothsurface of the hard carbon thin film.

Although the ECR plasma CVD technique was employed in the aboveExamples, the other techniques such as an RF plasma CVD technique mayalso be employed to form the hard carbon thin film.

In order to vary the sp² /sp³ ratio in a thickness direction of the hardcarbon thin film, several techniques are employed in the above Exampleswhich include varying the acceleration voltage applied to the grid,varying the supply amount of hydrogen introduced into the reactionchamber, and varying the substrate temperature. Another technique mayalso be employed to vary the sp² /sp³ ratio in a thickness direction ofthe hard carbon thin film, which varies a negative bias voltage producedby application of a high-frequency power to the substrate.Alternatively, the sp² /sp³ ratio can be varied in a thickness directionof the hard carbon thin film by introducing oxygen into a reactionsystem to thereby controlling development of sp² C--C bonding.

Although the vane, a sliding part of a rotary compressor, is used as thesubstrate in the above Examples, the present invention is not limitedthereto and other sliding parts including an electric shaver blade, amask for screen deposition and a squeegee may also be used as thesubstrate. Also, the hard carbon thin film of the present invention isapplicable for use as a constituent layer of a solar cell, a protectivecoating on a thin film magnetic head, and a protective or propagationfilm for surface acoustic wave devices.

Although the sliding part is described in the above Examples ascomprising high-speed tool steel, the material type of the sliding partis not limited thereto. Applicable materials include other steels,iron-based alloys, cast iron (MoNiChro cast iron), aluminum alloys,carbons (aluminum-impregnated carbon), ceramics (oxides, nitrides andcarbides of Ti, Al, Zr, Si, W, and Mo), Ni-based alloys, stainlesssteel.

In accordance with the first through fourth aspects of the presentinvention, the hard carbon thin film is provided which is high inhardness and assures excellent adherence to an underlying layer such asa substrate.

FIG. 17 is a schematic cross-sectional view showing an exemplaryapparatus for forming a hard carbon thin film in accordance with thefifth aspect of the present invention. Referring to FIG. 17, a vacuumchamber 28 is provided with a plasma generation chamber 24 to which oneend of a waveguide 22 is connected. A microwave supplying means 21 ismounted to another end of the waveguide 22. A microwave generated in themicrowave supplying means 21 passes through the waveguide 22 and amicrowave inlet window 23 to be guided into the plasma generationchamber 24. The plasma generation chamber 24 is provided with adischarge gas inlet line 25 for introducing a discharge gas such asargon (Ar) into the plasma generation chamber 24. A plurality of plasmamagnetic field generators 26 are mounted circumferentially of the plasmageneration chamber 24. A high density plasma can be generated within theplasma generation chamber 24 through the interaction of a high-frequencymagnetic field produced by the microwave and a magnetic field generatedby the plasma magnetic field generators 26. The vacuum chamber 28encloses a substrate holder 27 to which a high-frequency power source 30is connected for applying a bias voltage to a substrate during filmformation.

A substrate 33 is held on the substrate holder 27. A leading end of araw material gas supply tube 29 is located above the substrate holder 27for introducing into the vacuum chamber 28 a material gas for use information of a hard carbon thin film. Also disposed above the substrate33 is a filament 34 for thermally decomposing the raw material gassupplied from the raw material gas supply tube 29.

Positioned below the substrate holder 27 is a target 31 (Si target inthis Example) for use in formation of an interlayer. A high-frequencypower source 32 is connected to the target 31 to enable generation of anAr plasma between the substrate holder 27 and the target 31.

Examples will now be given below which utilize the apparatus shown inFIG. 17 in forming hard carbon thin films.

EXAMPLE 6

A silica glass is used as the substrate 33. Si is first deposited on thesubstrate 33 to form an interlayer. As shown in FIG. 18, the substrateholder 27 is rotated so that the substrate 33 is oriented to face towardthe target 31 located below the substrate 33. In this arrangement, thevacuum chamber 28 is evacuated to a pressure of 10⁻⁵ -10⁻⁷ Torr. Then,the Ar gas is supplied at 5.7×10⁻⁴ Torr. from the raw material gassupply tube 29. The high-frequency power source 32 supplies an RFvoltage to the target 31 to generate the Ar plasma between the target 31and the substrate holder 27. The target 31 is sputtered by ions in theplasma to form the interlayer (film thickness of 300 Å) comprised of Si.

Next, the substrate holder 27 is again rotated to return to its initialposition as shown in FIG. 17. In such a position, CH₄ and H₂ gases aresupplied from the raw material gas supply tube 29 at 5.0×10⁻⁴ Torr. and2.0×10⁻³ Torr., respectively. A voltage of 13 V is applied to thefilament 34 which is accordingly heated to a temperature of about 2000°C. Upon exposure to heat from the filament 34, the CH₄ gas is thermallydecomposed to result in formation of a diamond thin film on thesubstrate 33. The film formation is continued for about 5 minutes sothat the diamond film is formed on the substrate 33 to a thickness ofabout 500 Å, wherein the substrate temperature is increased to 400° C.

The subsequent reduction in the voltage applied to the filament allowsthe filament temperature to drop to 1000° C. from about 2000° C. Themicrowave supplying means 21 supplies a microwave at 2.45 GHz and 100 W.Concurrently, the Ar gas is supplied at 5.7×10⁻⁴ Torr. from thedischarge gas inlet line 25 to generate the Ar plasma within the plasmageneration chamber 24. The Ar plasma is directed onto the substrate 33.Simultaneously with this process, the high-frequency power source 30applies a 13.56 MHz RF voltage to the substrate holder 27 so that aself-bias voltage of -50 V is generated in the substrate, and the CH₄and H₂ gases are supplied at 1.3×10⁻³ Torr. and 2.0×10⁻² Torr.,respectively from the raw material gas supply tube 29. The CH₄ gas isdecomposed by the Ar plasma directed toward the substrate 33, and adiamond thin film is formed on the substrate 33. In this manner, thediamond thin film is deposited to a thickness of about 2000 Å. As aresult, the diamond thin film is formed on the substrate 33 to a totalthickness of about 2500 Å. The substrate temperature is in the range of250-300° C. during this process.

The results of Raman spectroscopic analysis revealed a sharp peak at1330 cm⁻¹ to demonstrate a typical diamond nature of the diamond thinfilm formed on the substrate 33. This diamond thin film was alsomeasured for hardness and surface roughness, the results of which aregiven in Table 1. The surface roughness was measured using acontact-type surface profile tester.

EXAMPLE 7

The procedure of Example 6 was repeated to form a thin film, except thatthe supply pressure of H₂ gas was reduced to a half of that used inExample 6. The results of Raman spectroscopic analysis revealed thesignificant increase in amount of amorphous components in the thin filmto demonstrate its structural shift, i.e. from a polycrystalline diamondthin film to a thin film containing amorphous components. Besides, thethin film obtained was measured for hardness and surface roughness, theresults of which are given in Table 1.

COMPARATIVE EXAMPLE 3

The diamond thin-film forming process of Example 6, which relied thethermal decomposition of the CH₄ gas on its exposure to heat from thefilament 34, was continued for about 25 minutes to form a diamond thinfilm having a thickness of about 2500 Å on the substrate 33, wherein thesubstrate temperature approached about 1000° C. The diamond nature ofthe thin film obtained was confirmed by Raman spectrum. The thin filmobtained was measured for hardness and surface roughness, the results ofwhich are given in Table 1.

                  TABLE 1                                                         ______________________________________                                                   Vickers  Surface                                                     Hardness (Hv) Roughness (μm)                                             ______________________________________                                        Exp. 6       8000       0.1                                                     Exp. 7 5000 0.05                                                              Comp.Exp. 3 9000 2                                                          ______________________________________                                    

As can be readily appreciated from Table 1, the film formation throughthermal decomposition of the raw material gas is able to provide a veryhard diamond thin film with a smooth surface when followed by the filmformation through both thermal and ECR plasma-assisted decomposition ofthe raw material gas. Also, although the substrate temperatureapproached 1000° C. in Comparative Example 3, as stated earlier, themaximum substrate temperature was 400° C. in Example 6, whichdemonstrates the ability of the combined film forming process to formthe diamond thin films at lower temperatures.

Also, it will be appreciated from the comparison between Examples 6 and7 that the regulated supply of the hydrogen gas enables the control ofamorphous components in the hard carbon thin films. That is, as thelarger amount of hydrogen gas is supplied, the more crystallinecomponents are incorporated in the resulting hard carbon thin film.Stated differently, as the smaller amount of hydrogen gas is supplied,the more amorphous components are incorporated in the resulting hardcarbon thin film.

EXAMPLE 8

In this example, subsequent to formation of a diamond thin film by usinga hot filament for thermally decomposing a raw material gas, the ECRplasma-assisted decomposition of the raw material gas was solelyeffected to form an additional thin film. That is, the procedure ofExample 6 was repeated to form a hard carbon thin film, except that thesubstrate was heated to about 400° C. using a heater accommodated in thesubstrate holder 27, instead of applying the voltage to the filament 34for heating thereof. The results of Raman spectroscopic analysisrevealed a sharp peak at 1330 cm⁻¹ to demonstrate a typical diamondnature of the hard carbon thin film obtained. This diamond thin film wasmeasured for hardness and surface roughness to exhibit values of 4500 Hvand 0.01 μm, respectively.

EXAMPLE 9

The procedure of Example 8 was followed to form a thin film, with theexception that the substrate temperature was maintained at roomtemperature during the film formation through the ECR plasma-assisteddecomposition of the material gas, i.e., no heating was applied to thesubstrate. The results of Raman spectroscopic analysis revealed a mainpeak at 1530 cm⁻¹ and a shoulder peak at 1400 cm⁻¹ to demonstrate atypical diamond-like nature of the thin film obtained. The diamond-likethin film obtained was measured for hardness and surface roughness, theresults of which are given in Table 2.

COMPARATIVE EXAMPLE 4

The procedure of Example 9 was followed to form a thin film, except thatthe diamond film forming process using a hot filament for thermallydecomposing the raw material gas was eliminated, an Si interlayer wasformed directly on the substrate, and the substrate temperature wasmaintained at room temperature during the film forming process throughthe ECR plasma-assisted decomposing of the material gas to form a thinfilm having a thickness of about 2500 Å on the Si interlayer. The thinfilm obtained was determined as being the diamond-like thin film. Thehardness and surface roughness of the thin film obtained are shown inTable 2.

                  TABLE 2                                                         ______________________________________                                                   Vickers  Surface                                                     Hardness (Hv) Roughness (μm)                                             ______________________________________                                        Exp. 9       3500       0.005                                                   Comp.Exp. 4 3000 0.004                                                      ______________________________________                                    

As can be readily appreciated from Table 2, the additional filmformation utilizing the ECR plasma subsequent to the film formationthrough the thermal decomposition of raw material gas, in accordancewith the fifth aspect of the present invention, enables the provision ofa very hard diamond-like thin film.

EXAMPLE 10

The procedure of Example 6 was repeated to form a diamond thin film,except that a voltage of 7 V was applied to the filament. The results ofRaman spectroscopic analysis demonstrated that the thin film obtainedcontained a higher proportion of amorphous components compared to thethin film obtained in Example 6. The thin film obtained was measured forhardness and surface roughness to exhibit values of 6000 Hv and 0.07 μm,respectively.

EXAMPLE 11

In this Example, the Ar and nitrogen gasses equal in amount weresupplied respectively at 5.7×10⁻⁴ Torr. to convert them into gas plasmaswhich sputtered the Si target to form an Si nitride interlayer. That is,the procedure of Example 11 was followed to form a diamond thin film,except that an Si nitride interlayer, instead of the Si interlayer, wasformed. The hardness and surface roughness of the diamond thin filmobtained were 8000 Hv and 0.1 μm, respectively.

EXAMPLE 12

In this Example, the Ar and oxygen gasses equal in amount were suppliedrespectively at 5.7×10⁻⁴ Torr. to convert them into gas plasmas whichsputtered the Si target to form an Si oxide interlayer. That is, theprocedure of Example 11 was followed to form a diamond thin film, exceptthat an Si oxide interlayer, instead of the Si interlayer, was formed.The hardness and surface roughness of the diamond thin film obtainedwere 8000 Hv and 0.1 μm, respectively.

EXAMPLE 13

In this Example, a hard carbon thin film having a graded structure ofvaried sp² /sp³ ratios in accordance with the first aspect of thepresent invention was formed utilizing a method in accordance with thefifth aspect of the present invention.

First, the vacuum chamber 28 was evacuated to a pressure of 10⁻⁵ -10⁻⁷Torr. Then, the Ar gas was supplied at 5.7×10⁻⁴ Torr. to produce the Arplasma between the target 31 and the substrate holder 27 so that ions inthe plasma sputtered the Si target, forming an Si interlayer.

After the Si interlayer forming process using a magnetron sputteringtechnique was terminated, the Ar gas was supplied at 5.7×10⁻⁴ Torr. fromthe discharge gas inlet line 25 of the ECR plasma generator.Concurrently, the microwave supplying means 21 supplied a microwave at2.45 GHz and 100 W to generate the Ar plasma within the plasmageneration chamber 24 for direction onto the substrate 33.Simultaneously with this process, the high-frequency power source 30applied a 13.56 MHz RF voltage to the substrate holder 27 so that aself-bias voltage of -50 V was generated in the substrate 33, and theCH₄ and H₂ gases were supplied at 1.3×10⁻³ Torr. and 2.0×10⁻² Torr.,respectively from the reactive gas supply tube 29. As a result, a hardcarbon thin film was formed to a thickness of 1000 Å.

Subsequent to termination of the above film-forming process using theplasma, the CH₄ and H₂ gases were supplied at 5.0×10⁻⁴ Torr. and2.0×10⁻³ Torr., respectively from the reactive gas supply tube 29, whilea voltage of 13 V was applied to the filament. The process was continuedfor about 10 minutes to form a diamond thin film having a thickness ofabout 1000 Å on the substrate 33.

Consequently, the hard carbon thin film was formed to a total thicknessof 2000° C.

In this Example, the hard carbon thin film thus obtained revealed thestructural transition from a thin film structure containing amorphouscomponents to a polycrystalline diamond thin film structure, i.e. thestructural transition from an sp² -rich film structure to an sp³ -richfilm structure in its thickness direction from the substrate/filminterface toward its surface.

In the above Example 7, the reduction of the H₂ gas supply pressureserved to increase in amount of the amorphous components in the hardcarbon thin film. However, the similar results can be attained byreducing the ECR plasma density. It is therefore possible to controlfilm properties by adjusting the plasma density.

Although it is described in the above Examples to form the interlayer onwhich the hard carbon thin film is subsequently formed, the fifth aspectof the present invention is not limited thereto, and includes the casewhere the hard carbon film is formed directly on the substrate.

Also, although the above Examples specify the thermal decomposition ofraw material gases as being effected by exposure to the hot filament,the fifth aspect of the present invention is not limited thereto.

Also, although the above Examples employ the film-forming techniquesolely through thermal decomposition of reactive gases in a firstfilm-forming step for forming an initial hard carbon thin film, thefifth aspect of the present invention is not limited thereto, andincludes an exemplary case where the first film-forming step relies thefilm formation on the decomposition of reactive gases by both heat andplasma. Also, where the film-forming process through decomposition ofthe reactive gases by both heat and plasma is carried out in both thefirst and second film-forming steps, the film-forming conditionsrespectively in the first and second steps may be varied from each otherto impart different proportions of crystalline and non-crystallinecomponents to the resulting hard carbon thin films.

FIG. 19 is a schematic cross-sectional view showing another exemplaryapparatus for forming a hard carbon thin film in accordance with thefifth aspect of the present invention. This apparatus is so constructedto be able to carry out a parallel-plate plasma CVD process. Thisapparatus is also enclosed in a vacuum chamber (not shown). As shown inFIG. 19, an electrode 41 is connected to a high-frequency power source45. A substrate 43 is placed on an opposite electrode 42 to which ahigh-frequency power source 46 is connected for supplying a bias voltageto the substrate 43. A raw material gas inlet 47 is located in thevicinity of the substrate 43 for supplying the raw material gastherefrom. Disposed between the electrode 41 and the opposite electrode42 is a filament 44 for exposing heat to the material gas to causedecomposition thereof.

The present invention is applicable not only to the ECR plasma CVDmethod, but also to the parallel-plate plasma CVD method as can beembodied using the apparatus of FIG. 19.

In accordance with the fifth aspect of the present invention, theproportion of crystalline and non-crystalline components in a hardcarbon thin film can be adjusted to provide controlled film properties,e.g. the controlled hardness and surface roughness of the hard carbonthin film. This not only permits formation of a crystalline diamond thinfilm with a smooth surface at relatively low temperatures, but alsopermits formation of a very hard amorphous diamond-like thin film.

FIG. 20 is a schematic cross-sectional view showing an exemplaryapparatus for forming an amorphous carbon coating in accordance with thesixth aspect of the present invention. The apparatus is capable ofcarrying out the ECR plasma CVD process to form the amorphous carboncoating, e.g. a diamond-like thin film, and is adapted to be able toproduce and emit ions or plasmas for surface cleaning.

Referring to FIG. 20, an upper interior portion of a vacuum chamber 57defines a plasma generation chamber 54 to which a microwave generator 51is connected through a waveguide 52. A microwave inlet window 53 isdisposed at the connection between the waveguide 52 and the plasmageneration chamber 54. The plasma generation chamber 54 is also equippedwith a discharge gas inlet line 55 for introducing a discharge gas suchas argon (Ar) into the plasma generation chamber 54. Plural plasmamagnetic field generators 56 are mounted circumferentially of the plasmageneration chamber 54.

A reaction chamber defined interior of the vacuum chamber 57 includes asubstrate holder 59 and is connected to a reactive gas inlet line 61 forintroducing a reactive gas into the vacuum chamber 57. A substrate 58 isheld on the substrate holder 59 to which a high-frequency power sourceis connected. An ion gun 62 is mounted interior of the vacuum chamber 57for emitting Ar ions toward the substrate 58.

The formation of the diamond-like thin film, as illustrative of theamorphous carbon coating, utilizing the apparatus shown in FIG. 20 isexplained by way of specific examples which follow.

EXAMPLE 14

First, the vacuum chamber 57 is evacuated to a pressure of 10⁻⁵ -10⁻⁷Torr. Then, the ion gun is operated to emit Ar ions to the substrate 58so that the substrate 58 is irradiated with the Ar ions for apredetermined time period. The ion emitting condition is set at an ioncurrent density of 0.3 MA/cm², an acceleration voltage of 400 eV, and anAr gas partial pressure of 3×10⁻⁵ Torr. In this example, the Ar ionirradiation was continued for 5 minutes, 10 minutes, 20 minutes, or 30minutes.

After the ion gun operation is discontinued, the Ar gas is supplied at5.7×10⁻⁴ Torr. from the discharge gas inlet line 55 of the ECR plasmagenerator. Concurrently, the microwave generator 51 supplies a microwaveat 2.45 GHz and 200 W to generate the Ar plasma within the plasmageneration chamber 54 for direction onto the substrate 58. The CH₄ gasis supplied at 1.3×10⁻³ Torr. from the reactive gas inlet line 61. TheCH₄ gas supplied from the reactive gas inlet line 61 is decomposed dueto the action of the Ar plasma to produce film-forming species which areconverted into highly reactive ions or neutral active species foracceleration onto a surface of the substrate 58. As a result, adiamond-like thin film is formed on the substrate 58. During the aboveprocess, the high-frequency power source 60 applies a 13.56 MHz RFvoltage to the substrate holder 59 so that a self-bias of -50 V isgenerated in the substrate 58.

The above leads to formation of the diamond-like thin film, i.e. theamorphous carbon coating on the substrate 58. The amorphous carboncoating is formed to a thickness of 100 Å, 500 Å, or 1000 Å.

For comparative purposes, the above procedure is followed to form on thesubstrate 58 an amorphous carbon coating to a thickness of 100 Å, 500 Å,or 1000 Å, except that no ion irradiation was effected.

The amorphous carbon coatings thus obtained were measured for surfaceroughness. The surface roughness was measured by a stylus-based testing(load: 30 mg, stylus travel speed: 25 sec/mm) using a stylus having aspherical point with a radius of about 2.5 μm, the results of which wereindicated by h_(rms) (root-mean-square deviation).

FIG. 21 is a graph showing the surface roughness of respective amorphouscarbon coatings having different thicknesses. As can be readilyappreciated from FIG. 21, the exposure of the substrate to ions emitted,prior to coating formation thereon, serves to impart a marked reductionin surface roughness to the resulting amorphous carbon coatings. Thesurface roughness of the resulting amorphous carbon coatings isdemonstrated as being maintained essentially constant if the ionirradiation is continued for the period exceeding 10 minutes. As alsoapparent from FIG. 21, when the cleaning treatment of substrate surfacewas performed prior to coating formation thereon in accordance with thesixth aspect of the present invention, the surface roughness of theresulting amorphous carbon coating was reduced to one fifth or less ofthe thickness thereof.

Next, among the amorphous carbon coatings obtained, the coatings formedon the substrate after irradiated with ions for 10 minutes were measuredfor coefficient of kinetic friction using a load of 20 g and an aluminaball of 10 mm in diameter. For comparative purposes, the amorphouscarbon coatings formed on the substrate which had not been exposed toions prior to coating formation thereon were also measured forcoefficient of kinetic friction. The measurement results are given inTable 3. In Table 3, "with ion irradiation" is intended to refer to thisExample, and "without ion irradiation" to Comparative Example.

                  TABLE 3                                                         ______________________________________                                                       Film Thickness                                                                  100Å  500Å                                                                             1000Å                                   ______________________________________                                        Friction   With Ion  0.10      0.15 0.13                                        Coefficient Irradiation                                                        Without Ion 0.12 0.18 0.17                                                    Irradiation                                                                ______________________________________                                    

As clearly shown in Table 3, the amorphous carbon coatings formed on therespective substrates which were cleaned at surfaces thereof byirradiation with ions prior to application of the coatings thereonexhibit lower friction coefficients at different film thicknessescompared to those of Comparative Example.

EXAMPLE 15

In this Example, the ion irradiation was effected during coatingformation to clean or etch a coating growth surface by bombardment ofhigh-velocity ions.

First, the vacuum chamber 57 is evacuated to a pressure of 10⁻⁵ -10⁻⁷Torr. Then, the ion gun is operated to emit Ar ions under the samecondition as in Example 14 to irradiate the substrate 58 with the Arions.

Concurrently, the Ar gas is supplied at 5.7×10⁻⁴ Torr. from thedischarge gas inlet line 55 and the microwave generator 51 supplies amicrowave at 2.45 GHz and 200 W to generate the Ar plasma within theplasma generation chamber 54 for direction onto the substrate 58. TheCH₄ gas is supplied at 1.0×10⁻³ Torr. from the reactive gas inlet line61. The CH₄ gas supplied from the reactive gas inlet line 61 isdecomposed due to the action of the Ar plasma to produce film-formingspecies which are converted into highly reactive ions or neutral activespecies for acceleration onto a surface of the substrate 58. As aresult, an amorphous carbon coating is deposited on the substrate 58.

As analogously to Example 14, the high-frequency power source 60 appliesa 13.56 MHz RF voltage to the substrate holder 59 so that a self-bias of-50 V is generated in the substrate 58 during the above process.

The amorphous carbon coating is formed to a thickness of 100 Å, 500 Å,or 1000 Å. The amorphous carbon coatings thus obtained were measured forsurface roughness in the same manner as in Example 14, the results ofwhich are given in Table 4. Also, for comparative purposes, theamorphous carbon coatings formed without ion irradiation duringformation thereof were also measured for surface roughness, the resultsof which are also given in Table 4.

                  TABLE 4                                                         ______________________________________                                                       Film Thickness                                                                  100Å  500Å                                                                             1000Å                                   ______________________________________                                        Friction   With Ion  10Å    45Å                                                                            88Å                                    Coefficient Irradiation                                                        Without Ion 25Å 115Å 220Å                                         Irradiation                                                                ______________________________________                                    

As can be appreciated from Table 4, cleaning or etching the coatinggrowth surface by exposure thereof to the Ar ions during coatingformation, in accordance with the sixth aspect of the present invention,serves to impart reduced surface roughness, i.e. increased surfacesmoothness to the resulting amorphous carbon coating.

EXAMPLE 16

In this Example, a plasma treatment was performed to clean or etch thesubstrate surface.

First, the vacuum chamber 57 was evacuated to a pressure of 10⁻⁵ -10⁻⁷Torr. Then, the Ar gas is supplied at 5.7×10⁻⁴ Torr. from the dischargegas inlet line 55, while the microwave generator 51 supplies a microwaveat 2.45 GHz and 200 W, to generate the Ar plasma within the plasmageneration chamber 54. Concurrently, the high-frequency power source 60applies a 13.56 MHz RF voltage to the substrate holder 59 so that aself-bias voltage of -50 V is generated in the substrate 58. The Arplasma generated within the plasma generation chamber 54 is therebyaccelerated onto a surface of the substrate 58 to effect cleaning of thesubstrate surface. After irradiation with the Ar plasma for 10 minutes,an amorphous carbon coating is formed on the substrate in the samemanner as in Example 14.

The amorphous carbon coating is formed to a thickness of 100 Å, 500 Å,or 1000 Å. The amorphous carbon coatings thus obtained were measured forsurface roughness in the same manner as in Example 14, the results ofwhich are given in Table 5.

                  TABLE 5                                                         ______________________________________                                                       Film Thickness                                                                  100Å  500Å                                                                             1000Å                                   ______________________________________                                        Friction   With Ion  10Å    45Å                                                                            88Å                                    Coefficient Irradiation                                                        Without Ion 25Å 115Å 220Å                                         Irradiation                                                                ______________________________________                                    

As can be appreciated from Table 5, cleaning or etching the substratesurface by irradiation with the Ar plasma prior to coating formationthereon also serves to impart reduced surface roughness, i.e. increasedsurface smoothness to the resulting amorphous carbon coating.

In summary, the hard carbon thin films having excellent surfacesmoothness can be formed in accordance with the fifth or sixth aspect ofthe present invention, which accordingly have utilities as for coatingmaterials and the others.

The hard carbon thin film formed in accordance with the presentinvention can provide excellent characteristics when applied, forexample, to shaver blades, thin-film magnetic heads, magneto-opticaldisks, sliding parts for compressors, antireflection coatings for use inthe manufacture of semiconductors, heat sinks for semiconductor devices,surface acoustic wave devices.

What is claimed is:
 1. A hard carbon thin film arrangement comprising ahard carbon thin film having a surface and an interface opposite saidsurface with a thickness direction extending through said thin film fromsaid interface to said surface, and having a graded carbon compositionin which a ratio of sp² to sp³ carbon-carbon bonding in said thin filmdecreases in said thickness direction from said interface to a minimumat an internal location of said thin film between said interface andsaid surface, and increases from said minimum at said internal locationtoward said surface of said thin film.
 2. The hard carbon thin filmarrangement of claim 11, wherein said thin film comprises at least twolayers having respective individual sp² /sp³ carbon-carbon bondingratios different from each other so that said ratio of sp² to sp³carbon-carbon bonding in said thin film decreases in said thicknessdirection in a stepwise manner from said interface to said minimum atsaid internal location and increases therefrom in a stepwise mannertoward said surface of said thin film.
 3. The hard carbon thin filmarrangement of claim 1, wherein said ratio of sp² to sp³ carbon-carbonbonding is varied in the range of -0 to
 3. 4. The hard carbon thin filmarrangement of claim 1, wherein said hard carbon thin film is acrystalline diamond carbon thin film, an amorphous diamond-like carbonthin film, or a diamond-like carbon thin film having a partialcrystalline structure.
 5. The hard carbon thin film arrangement of claim1, further comprising a substrate and an interlayer between said thinfilm and said substrate, wherein said interface of said thin film is incontact on said interlayer.
 6. The hard carbon thin film arrangement ofclaim 5, wherein said interlayer comprises at least one materialselected from the group consisting of Si, Ti, Zr, W, Mo, Ru, Ge, andoxides, nitrides, and carbides thereof.
 7. A method for forming the hardcarbon thin film arrangement of claim 1, using a plasma CVD technique,comprising imparting and varying an acceleration energy to film-formingion species in a plasma so as to change kinetic energies thereof duringa film-forming time while depositing said ion species, thereby formingsaid graded carbon composition of said thin film.
 8. A method forforming the hard carbon thin film arrangement of claim 1 using a plasmaCVD technique, comprising admitting and varying an amount of a hydrogengas in a reaction system during a film-forming time while depositingsaid thin film, thereby forming said graded carbon composition of saidthin film.
 9. A method for forming the hard carbon thin film arrangementof claim 1 using a plasma CVD technique, comprising varying a substratetemperature during a film-forming time while depositing said thin film,thereby forming said graded carbon composition of said thin film.
 10. Amethod for forming the hard carbon thin film arrangement of claim 1using a plasma CVD technique, comprising supplying varying film-formingion species during a film-forming time while depositing said ionspecies, thereby forming said graded carbon composition of said thinfilm.
 11. A method for forming the hard carbon thin film arrangement ofclaim 1 using a plasma CVD technique, comprising carrying out acombination of a first film-forming process through thermaldecomposition of a raw material gas and a second film-forming processthrough plasma-assisted decomposition of said raw material gas, in sucha manner so as to form said graded carbon composition.
 12. A hard carbonthin film having a surface exhibiting a surface roughness h_(rms) of notmore than one fifth of a thickness of said thin film immediately afterformation thereof.
 13. The hard carbon thin film of claim 12, whereinsaid surface roughness is not more than one tenth of said thickness ofsaid thin film.